[crankshaft] Don't inline the fast path for instanceof if the function has a non-instance .prototype

test/mjsunit/regress/regress-crbug-666308.js

Index: test/mjsunit/regress/regress-crbug-666308.js
diff --git a/test/mjsunit/regress/regress-crbug-666308.js b/test/mjsunit/regress/regress-crbug-666308.js
new file mode 100644
index 0000000000000000000000000000000000000000..5e0e3746bb9be456bba1cd97fee531982226746a
--- /dev/null
+++ b/test/mjsunit/regress/regress-crbug-666308.js
@@ -0,0 +1,9 @@
+// Copyright 2016 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+function foo() {}
+foo.prototype = 1;
+v = new foo();
+function bar() { return v instanceof foo; }
+assertThrows(bar);